Most diabetic patients, due to the complications of their disease, suffer from nerve damage or neuropathy in their extremities, such as their feet, which results in a loss of tactile sensation. This loss of tactile sensation can lead to the formation of ulcers or open wounds in the layers of skin of a patient's feet. Recently, it has been determined that such foot ulcers are related to the application of normal forces and shear forces on the plantar portion or bottom surface of the patient's foot.
As such, a variety of measurement systems have been developed in an attempt to detect the forces that are applied to a diabetic's feet, in real-time, using load sensors and pressure sensors. For example, the F-Scan® system and Pedar® system, which use pressure-sensor arrays, have been used to measure the pressure distribution on a person's feet. The disadvantage of these force-measurement systems is that while they are sensitive to normal forces, they are insensitive to shear forces. Other sensor-array devices have also been developed, which are able to detect normal forces and shear forces simultaneously. However, such sensor-array devices are bulky in size, making its attachment to a patient's feet impractical. In addition, compact sensors have also been developed, which overcomes these drawbacks and integrates two shear sensors and an F-Scan® pressure sensor distribution sensor into an insole of a shoe. However, due to the complexity of its design, such a device is extremely high in cost, and therefore many diabetic patients who could benefit from a wearable force monitoring device are unable to afford its cost.
Therefore, there is a need for a miniature inductive-force sensor for dynamic, simultaneous measurement of normal and shear forces that are applied to a diabetic's feet, which is low cost. In addition, there is a need for a miniature inductive-force sensor that is configured to provide real-time monitoring of normal and shear forces that are applied to a person's feet. Furthermore, there is a need for a miniature inductive-force sensor that is configured to be mounted on or integrated into in an insole of a shoe. Additionally, there is a need for a miniature inductive-force sensor that is capable of simultaneous measurement of normal force and two-axis shear force using only one set of measurement circuitry, thereby making the inductive-force sensor compact in size.